Moleclar Epidemiology Of Porcine Circovirus Type2 Isolates Collected In Some Areas Of China

Diseases caused by Porcine circovirus type 2 (PCV2) mainly included postweaning multisystemic wasting syndrome (PMWS), procine dermititis and nephropathy syndrome (PDNS), procine respiratory disease syndrome (PRDC), congenital tremor syndrome, reproductive failure and procine proliferative and necrotizing pneumonia. PCV2 is widespread both at home and abroad, and it resulted in growth retardation of swine and reduced profit. With immunosuppression caused by PCV2 infection, immunity of swine decreased and secondary infection probably occurred. Diseases associated with PCV2 could cause large economic loss in worldwide pig industry besides the pig industry of China. On basis of differences of antigenicity and genome composition, PCV was divided into two serotypes, PCV1 and PCV2. In most reports, PCV1 was mentioned to be non-pathogenic but widespread in herds. Some groups validated there were two genotypes within PCV2, named PCV2a and PCV2b. The both are prevalent in the United States, Canada and some European countries.In our study, 235 PCV-positive samples from 11 provinces of China were genotyped by differential PCR test, The results demonstrated that 10 of 235 isolates were PCV2a and the rate was 4.2%; 133 of 235 isolates were PCV2b and the rate was 56.6%. Therefore, PCV2a and PCV2b are prevalent in China and PCV2 is the predominant genotype.In addition, genomes were amplified from PCV2-positive isolates from 6 provinces of China by PCR test. 37 recombinant plasmids containing individual genome of PCV2 were obtained and the results of sequencing shown that the length of PCR products were 1767bp and 1768bp. The representative entire nucleotide sequences of 10 of 37 PCV2 isolates were published in GeneBank. Using BioEdit and DNAStar software, sequences of 10 PCV2-positive isolates were compared with those of other PCV2 isolates in the GenBank, sequences homology of isolates was from 94.3% to 99.7% .Moreover, Nucleotide sequence of PCV2a isolates were compared with those of American isolates EU594437 and Japanese isolates AB426905 and sequences homology was 96.7% and 99.0%, respectively. And the amino acid sequence alignment of the capsid protein encoded by ORF2 gene showed Chinese PCV2 strains exhibited three major regions of greater heterogeneity at residues 53～92aa,121～136aa and 190～215aa, amino-acids position is related to the epitopes spanning residues. The whole 37 PCV2-positive isolates compared by MEGA4.1 software and then the phylogenetic trees were drawn. Phylogenetic tree could be divided into three main branches, PCV2a, PCV2b and unknown PCV2c, however, PCV2c need to be further validated.